Conventionally, the illumination systems used in most projection apparatuses are for example ultra-high pressure (UHP) mercury lamps. Recently, light emitting diodes (LED) and laser diodes are gradually used as the illumination systems of the projection apparatuses. While designing the illumination system, the color of the projection image and the use life are taken into consideration. Generally, the illumination system comprises a light source and a color wheel. During operation of the illumination system, a light source emits a single color beam to the color wheel and thus three primary color lights RGB are produced. In the conventional laser projection apparatus, the illumination system further comprises the color wheel and an additional phosphor wheel. When a laser light source emits a laser beam to excite a phosphor powder of the phosphor wheel, a color light with a different wavelength is produced. Consequently, the three primary color lights RGB can be produced. However, the heat dissipation mechanism of the illumination system of the laser projection apparatus is an important factor influencing the use life of the illumination system. Conventionally, the heat dissipation mechanism introduces a cooling gas into the illumination system in order to remove the heat from the illumination system. However, while the cool airflow is inhaled into the illumination system, external dust is readily introduced into the internal portion of the illumination system along with the airflow. Under this circumstance, the performance of the phosphor wheel is deteriorated, and thus the use life of the illumination system reduces.
For preventing the contamination of the particulate dust, the illumination system is usually equipped with a filter for filtering the particulate dust of the airflow. Moreover, the filtered particulate dust is collected by a dust bag. As known, the pore size of the filter is an important factor. In case that the pore size of the filter is too large, the filter is unable to effectively retain the dust. Whereas, in case that the pore size of the filter is too small, the flow rate of the airflow is largely reduced. Under this circumstance, the heat cannot be effectively removed by the airflow. Moreover, since the filter is usually installed within the illumination system, the user cannot visually realize whether the accumulated dust of the filter is serious and whether the filter needs to be replaced. If the accumulated dust of the filter is serious and the filter is not replaced with a new one, the dust collecting efficiency of the filter is impaired and the heat dissipating efficiency is deteriorated.
Nowadays, an infrared detecting technology is used to detect whether the dust collecting level of the dust bag reaches a preset level. However, as the dust collecting level of the dust bag increases, the dust bag is subjected to irregular deformation. The infrared detecting technology detects whether an optical path of an infrared ray is obstructed by the expanded volume of the dust bag so as to judge whether the dust collecting level of the dust bag reaches the preset level. Owing to the irregular deformation of the dust bag, the infrared detecting technology may have a misjudgment problem. Moreover, since the filter and the dust bag are fixed within the projection apparatus, the user cannot replace the filter and the dust bag. In other words, for replacing the filter or the dust bag, the user has to send the projection apparatus to the manufacturer or the maintenance center.